The present invention relates to an actuator device.
Such a device is known for example from EP 1 760 796 B1 and describes the use of an expansion element of a magnetic shape memory alloy material (MSM=magnetic shape memory, used here below synonymously with the German abbreviation magnetic FGL=Formgedächtnislegierung [shape memory alloy]) for the desired actuator- or respectively actuating device. In practical terms, for effecting this drive, an MSM(FGL) crystal body, typically produced on the basis of an NiMnGa alloy, is acted upon by a magnetic field generated by an energized coil. As a reaction to such a magnetic flow (typically introduced on the casing side), the MSM crystal body carries out, as expansion unit, an expansion movement, the stroke of which usually runs in a direction perpendicularly to the magnetomotive force direction with the magnetic flow. This expansion movement then acts on a ram adjoining on the end side along the expansion- or respectively actuating direction, which in turn, corresponding to a respective actuating task, interacts with a suitable actuating partner.
Generally, actuators based on MSM have the advantage of quick switching times and high switching cycles (so-called switching operation number, which can comprise more than 400 million expansion processes). MSM expansion units used for actuating elements and expandable as a reaction to the introduced magnetic flow enable a typical expansion stroke in the order of approximately 4% to 6% in relation to the actuating- or respectively expansion direction (in the non-expanded state), wherein the crystal body usually elongated in this direction is supported on its face side lying opposite the ram unit or respectively is fixed there and receives on the casing side the magnetic flow introduced by flow conducting means.
FIG. 2 for the diagrammatically illustrated prior art, presupposed as being known, illustrates a problem resulting from this operating principle: An MSM crystal body 10 as expansion unit, supported on the base side in a suitable manner, is acted upon via a pair of flow conducting bodies 12, 14 engaging on the casing side with a magnetic flow H (running in the plane of the figure transversely and thereby perpendicularly to the longitudinal axis) for expansion. As in practice a completely homogeneous magnetic flow input into the expansion body 12 is only rarely possible, and the latter, in order to enable an efficient expansion, must be guided with clearance within the flow conducting structure 12, 14, an oblique position or respectively a tilting of the expansion crystal 10 occurs, as shown diagrammatically in FIG. 2. The consequence are disadvantageous frictional forces FR at the contact surfaces, occurring through the oblique position, to the flow conducting elements 12, 14, with the result that friction influences the dynamic characteristics and the efficiency of the actuator device subsequently and in addition wear- or respectively so-called tribocorrosion occurs especially at the ends of the expansion body. Even (local) deformation effects on the MSM element are possible, with the disadvantageous consequence that the operational behaviour or respectively the lifespan of the device is impaired.
Additionally disadvantageously, the end face, directed on the engagement side (i.e. onto an interacting ram unit 16, which is guided, shown diagrammatically, against the force of a return spring 18 in an actuator housing 20) in the transition region 22 to the ram 16 engages eccentrically and thereby in a punctiform manner onto the ram, creates potentially harmful friction here and leads, in addition, to a (typically oppositely directed) tilting of the ram unit 16 within its guide (i.e. associated with the ram). With a play which is also necessarily present here, therefore the disadvantageous tilting of the expansion unit from the ideal actuating direction has a disadvantageous effect on the downstream ram unit.
A further disadvantageous effect of the oblique position, shown in FIG. 2, occurring on introduction of the magnetic flow H is the fact that the magnetic field (with assumed flow lines running in an ideal parallel manner) no longer meets perpendicularly onto the corresponding, associated lateral face of the MSM expansion unit 10, the crystalline main axes of which, however, are directed parallel to the edges or respectively lateral faces. Accordingly, an angular deviation of the magnetic field from the (ideal) normal occurs, which as a result leads to an increase of the current required for the magnetic flow, in order to bring about an actuator movement (switching) of the actuator. The effect that the shown oblique position favours an oblique field line course (namely in the plane of the figure of FIG. 2 from top left to bottom right) and thereby a field component in oblique direction, also has a disadvantageous and current-increasing effect, because the magnetic resistance at the friction- or respectively contact sites is lowered and thus the air gap between expansion unit and surrounding flow-conducting structure is bridged.
In the technical teaching described in EP 1 760 796 B1 the MSM expansion unit is guided in a lateral guide (typically realized by means of a groove), wherein the groove lies in a neutral, geometrically non-altering plane. This technical measure in fact prevents or makes difficult the previously described disadvantageous tilting, but is itself again disadvantageous: In fact, in the case of optimum dimensioning and the best possible tolerance configuration, the MSM unit is held in its position defined by the groove, but friction between the expansion unit and the flow-conducting means interacting therewith is not prevented, rather this friction is displaced to the groove region of the MSM expansion unit. Therefore, it is to be expected that wear occurs here, which in turn, directly critically in this relatively delicate mechanical configuration, significantly shortens the lifespan. The technology described in EP 1 760 796 B1 is also tolerance-susceptible, because for preventing tilting or suchlike blocking behaviour the shape and position of the grooves (in interaction with the outer guide partners) must be manufactured precisely.
Finally, this known technical teaching is disadvantageous with regard to the effect that, depending on the microstructure of the MSM body realizing the expansion unit, during the switching process a bend of approximately 3° runs through the element; already this effect makes a geometrically fixed “neutral” mounting according to EP 1 760 796 B1 impracticable.
It is therefore an object of the present invention to improve a generic actuator device with regard to its expansion- and efficiency behaviour, in particular to prevent or reduce a friction, effected during the expansion movement of the expansion unit, on associated lateral flow-conducting means and/or on the ram unit, to prevent or reduce corresponding wear and to thus create a device which combines improved dynamics- and actuating characteristics with increased lifespan, reduced current consumption and increased switching operation numbers.